A. An undesirable constituent of air​

Why does earth rotate? because earth is formed from cold gases collapsing due to gravity because the matter in the nebula that formed earth was spinning because earth forms more than 99% of the mass of the solar system because the hydrogen atoms inside the nebula fused to form helium

As changes in energy levels of electrons increase, the frequencies of atomic line spectra they emit

•hydration •dissociation •dissolving which one goes to which